#include <stdio.h>
#include <stdlib.h>

typedef struct ListNode
{
    int val;
    struct ListNode* next;
}ListNode;


struct ListNode* FindKthToTail(struct ListNode* pListHead, int k) {
    struct ListNode* slow = pListHead, * fast = pListHead;
    int tem = k;
    while (k--) {
        if (!fast)
            return NULL;
        fast = fast->next;
    }

    while (fast) {
        slow = slow->next;
        fast = fast->next;
    }
    return slow;
}


int main()
{
    struct ListNode* n1 = (struct ListNode*)malloc(sizeof(struct ListNode));
    struct ListNode* n2 = (struct ListNode*)malloc(sizeof(struct ListNode));
    struct ListNode* n3 = (struct ListNode*)malloc(sizeof(struct ListNode));
    struct ListNode* n4 = (struct ListNode*)malloc(sizeof(struct ListNode));
    struct ListNode* n5 = (struct ListNode*)malloc(sizeof(struct ListNode));
    struct ListNode* n6 = (struct ListNode*)malloc(sizeof(struct ListNode));

    n1->val = 1;
    n2->val = 2;
    n3->val = 3;
    n4->val = 4;
    n5->val = 5;
    n6->val = 6;

    n1->next = n2;
    n2->next = n3;
    n3->next = n4;
    n4->next = n5;
    n5->next = n6;
    n6->next = NULL;

    ListNode* ret = FindKthToTail(n1, 2);
    printf("%d\n", ret->val);

    return 0;
}